Methods for transmitting and receiving control channel in wireless communication systems

ABSTRACT

A method of transmitting and receiving a control channel in a wireless communication system is provided. A base station allocates a data channel to a radio resource, adds start position information of the data channel into a payload of a control channel, and performs signaling for indication information on the start position information added into the payload of the control channel to a terminal. Accordingly, the legacy system and the enhanced system can efficiently transmit a control channel.

CLAIM FOR PRIORITY

This application is a continuation of U.S. application Ser. No.13/529,310, filed Jun. 21, 2012, which claims priority to Korean PatentApplication Nos. 10-2011-0060191 filed on Jun. 21, 2011, 10-2011-0081043filed on Aug. 16, 2011, 10-2011-0086737 filed on Aug. 29, 2011,10-2011-0102910 filed on Oct. 10, 2011, and 10-2012-0009514 filed onJan. 31, 2012, in the Korean Intellectual Property Office (KIPO), theentire contents of which are hereby incorporated by reference.

BACKGROUND 1. Technical Field

Example embodiments of the present invention relate in general to awireless communication system, and more specifically to a method oftransmitting and receiving a control channel in a wireless communicationsystem.

2. Related Art

A data transmission rate in wireless communication systems and wiredcommunication systems has recently become very high. In line with thistrend, the 3^(rd) generation project partnership long term evolution(3GPP LTE) system and the LTE-advanced system are presently undergoingstandardization.

In the 3GPP LTE system, downlink transmission is based on orthogonalfrequency division multiplexing (OFDM), and uplink transmission is basedon single frequency-frequency division multiple access (SC-FDMA).

That is, the 3GPP system uses time-frequency resources as fundamentalphysical resources, and each resource element corresponds to one OFDMsubcarrier during one OFDM symbol period. Also, downlink subcarriers aregrouped into a plurality of resource blocks in a frequency domain, andeach of the resource blocks consists of twelve successive subcarriers.

In the 3GPP LTE system, the physical downlink shared channel (PDSCH) isused as a physical channel for transmitting downlink unicast data, andthe physical uplink shared channel (PUSCH) is used as a downlinkphysical data channel for transmitting uplink data. Also, the physicaldownlink control channel (PDCCH) is used as a downlink physical controlchannel for transmitting downlink control information, such asscheduling necessary for receiving the PDSCH, and scheduling approvalfor transmission in the PUSCH. The downlink physical data channel andthe downlink physical control channel are mapped in units of subframescomprising time-frequency resources.

When a data channel and a control channel are multiplexed in onesubframe, a base station provides start position information of the datachannel in a time domain, for which an efficient method is required.

Moreover, when the enhanced PDCCH (ePDCCH) allocated to a data channelregion of a subframe is introduced, an efficient control channeltransmission method is necessary for both an enhanced system capable oftransmitting/receiving the ePDCCH and a legacy system incapable oftransmitting/receiving the ePDCCH.

SUMMARY

Accordingly, example embodiments of the present invention are providedto substantially obviate one or more problems due to limitations anddisadvantages of the related art.

Example embodiments of the present invention provide a method ofefficiently transmitting and receiving a control channel in a wirelesscommunication system.

In some example embodiments, a method of transmitting and receiving acontrol channel includes: allocating a data channel to a radio resource;adding start position information of the data channel into a payload ofa control channel; and signaling indication information on the startposition information added into the payload of the control channel.

The adding of start position information may include defining a bitfield for the start position information in the payload, and adding thestart position information into the bit field.

The adding of start position information may include adding the startposition information into an unused bit field among bit fields of thepayload.

The adding of start position information may include inserting a CRCvalue, which is obtained by applying a predefined mask value to CRC ofthe payload, into the payload according to the start positioninformation.

The adding of start position information may include inserting a resultof performing a modulo operation using the predefined mask value, an IDof a terminal, and the CRC of the payload, into the payload according tothe start position information.

The data transmission apparatus may not allocate at least one ID equalto a quantity of start position information to another terminal suchthat the CRC values of the terminal and the other terminal do notoverlap.

The adding of start position information may include: additionallyallocating different temporary IDs to a terminal according to the startposition information; calculating a CRC value corresponding to the startposition information by using the additionally allocated temporary IDs;and inserting the calculated CRC value into the payload.

A temporary ID first allocated to the terminal may indicate specificstart position information, and the start position information may bepredefined between the base station and the terminal.

The adding of start position information may include applying differentscrambling sequences to the payload of the control channel according tothe start position information.

Each of the scrambling sequences may be generated on the basis ofdifferent sequence initial values that are predefined between the datatransmission apparatus and a terminal according to the start positioninformation.

In other example embodiments, a method of transmitting and receiving acontrol channel in a wireless communication system, including aplurality of data transmission apparatuses, includes: transmitting, byat least one first data transmission apparatus, a data channel to aterminal; and transmitting, by a second data transmission apparatus, acontrol channel to the terminal, wherein the second data transmissionapparatus transmits MBSFN subframe information as information on the atleast one first data transmission apparatus.

The transmitting of a control channel may include: defining, by thesecond data transmission apparatus, a bit field for the MBSFN subframeinformation in a payload of the control channel; and adding, by thesecond data transmission apparatus, bitmap information into the bitfield, the bitmap information indicating whether the at least one firstdata transmission apparatus includes MBSFN subframe information.

In still other example embodiments, a control channel transmission andreception method for transmitting an enhanced downlink physical controlchannel, which is added into a section of a downlink physical datachannel and transmitted, includes: allocating at least one downlinkdemodulation reference signal to a first symbol other than a secondsymbol to which a downlink cell-specific reference signal has beenallocated, in a subframe, the first symbol being included in anfrequency domain to which at least one control channel elementconfiguring the enhanced downlink physical control channel has beenallocated; and transmitting the subframe.

The allocating of at least one downlink demodulation reference signalmay include allocating a control channel element instead of the downlinkcell-specific reference signal to the frequency domain to which the atleast one control channel element has been allocated, when the subframeis an MBSFN subframe.

In still other example embodiments, a control channel transmission andreception method of a data transmission apparatus includes: configuringa search space in which an enhanced downlink physical control channelcandidate consists of adjacent control channel elements (CCEs), in atleast one aggregation level, the enhanced downlink physical controlchannel denoting a physical control channel that is added into adownlink physical data channel region and transmitted; and providinginformation of the configured search space to a terminal.

The configuring of a search space may include: allocating differentenhanced downlink physical control channel candidates by aggregationlevel; setting a CCE-unit offset between the enhanced downlink physicalcontrol channel candidates by aggregation level; and setting a CCE-unitoffset for each terminal by aggregation level.

In still other example embodiments, a data channel transmission andreception method of a data transmission apparatus includes: configuringa search space by configuring an enhanced downlink physical controlchannel candidate with distributed control channel elements (CCEs), inat least one aggregation level, the enhanced downlink physical controlchannel denoting a physical control channel that is added into adownlink physical data channel region and transmitted; and providinginformation of the configured search space to a terminal.

The configuring of a search space may include setting a CCE-unit offsetbetween the at least one CCE configuring the enhanced downlink physicalcontrol channel candidate.

In still other example embodiments, a control channel transmission andreception method of a data transmission apparatus includes: determininga kind of a control channel for transmitting control information and atransmission type of the control channel according to whether to enablereception of an enhanced downlink physical control channel and fallbackcontrol information and control information based on a physical datatransmission mode, the enhanced downlink physical control channeldenoting a physical control channel that is added into a downlinkphysical data channel region and transmitted; and configuring a controlchannel on the basis of the determined kind and transmission type of thecontrol channel.

The determining of a kind of a control channel may include: determiningone of a downlink physical control channel and the enhanced downlinkphysical control channel as the kind of the control channel; anddetermining one of a localized type, in which a search space isconfigured for control channel elements of the control channel to beadjacent, and a distributed type, in which a search space is configuredfor the control channel elements to be distributed, as the transmissiontype of the control channel.

According to the methods of transmitting and receiving a control channelin the wireless communication system, provided are various methods thatprovide the start position information of the data channel by using theallocation information control channel. Also, provided are variousmethods of configuring an enhanced downlink physical control channel,and provided are a search space configuration method for a legacy systemand an enhanced system and a method of transmitting control informationthat is transmitted through a search space.

Therefore, base stations and terminals can effectively transmit andreceive a control channel in both an enhanced system with an enhanceddownlink physical control channel applied thereto and a legacy system towhich the enhanced downlink physical control channel is not applied.

BRIEF DESCRIPTION OF DRAWINGS

Example embodiments of the present invention will become more apparentby describing in detail example embodiments of the present inventionwith reference to the accompanying drawings, in which:

FIG. 1 is a conceptual diagram illustrating an example of a wirelesscommunication environment in which it is necessary to explicitlytransmit start position information;

FIG. 2 is a conceptual diagram illustrating another example of awireless communication environment in which it is necessary toexplicitly transmit start position information;

FIG. 3 is a conceptual diagram illustrating a configuration of adownlink subframe that is used in a method of transmitting and receivinga control channel according to an embodiment of the present invention;

FIG. 4 is a conceptual diagram illustrating an example of a normalsubframe applied to the method of transmitting and receiving a controlchannel according to an embodiment of the present invention;

FIG. 5 is a conceptual diagram illustrating another example of a normalsubframe applied to the method of transmitting and receiving a controlchannel according to an embodiment of the present invention;

FIG. 6 is a conceptual diagram illustrating another example of a normalsubframe applied to the method of transmitting and receiving a controlchannel according to an embodiment of the present invention;

FIG. 7 is a conceptual diagram illustrating another example of a normalsubframe applied to the method of transmitting and receiving a controlchannel according to an embodiment of the present invention;

FIG. 8 is a conceptual diagram illustrating another example of a normalsubframe applied to the method of transmitting and receiving a controlchannel according to an embodiment of the present invention;

FIG. 9 is a conceptual diagram illustrating another example of a normalsubframe applied to the method of transmitting and receiving a controlchannel according to an embodiment of the present invention;

FIG. 10 is a conceptual diagram illustrating another example of a normalsubframe applied to the method of transmitting and receiving a controlchannel according to an embodiment of the present invention;

FIG. 11 is a diagram illustrating a configuration example of a localizedtype search space applied to the method of transmitting and receiving acontrol channel according to an embodiment of the present invention;

FIG. 12 is a diagram illustrating another configuration example of alocalized type search space applied to the method of transmitting andreceiving a control channel according to an embodiment of the presentinvention;

FIG. 13 is a diagram illustrating another configuration example of alocalized type search space applied to the method of transmitting andreceiving a control channel according to an embodiment of the presentinvention;

FIG. 14 is a diagram illustrating another configuration example of alocalized type search space applied to the method of transmitting andreceiving a control channel according to an embodiment of the presentinvention;

FIG. 15 is a diagram illustrating a configuration example of adistributed type search space applied to the method of transmitting andreceiving a control channel according to an embodiment of the presentinvention;

FIG. 16 is a diagram illustrating another configuration example of adistributed type search space applied to the method of transmitting andreceiving a control channel according to an embodiment of the presentinvention;

FIG. 17 is a diagram illustrating another configuration example of adistributed type search space applied to the method of transmitting andreceiving a control channel according to an embodiment of the presentinvention; and

FIG. 18 is a diagram illustrating another configuration example of adistributed type search space applied to the method of transmitting andreceiving a control channel according to an embodiment of the presentinvention.

DESCRIPTION OF EXAMPLE EMBODIMENTS

The invention may have diverse modified embodiments, and thus, exampleembodiments are illustrated in the drawings and are described in thedetailed description of the invention.

However, this does not limit the invention within specific embodimentsand it should be understood that the invention covers all themodifications, equivalents, and replacements within the idea andtechnical scope of the invention. Like numbers refer to like elementsthroughout the description of the figures.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”,“comprising,”, “includes” and/or “including”, when used herein, specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

A terminal used in the specification may refer to user equipment (UE), amobile station (MS), a relay node (RN), a machine type communication(MTC) device, a mobile terminal (MT), a user terminal (UT), a wirelessterminal, an access terminal (AT), a terminal, a subscriber unit, asubscriber station (SS), a wireless device, a wireless communicationdevice, a wireless transmit/receive unit (WTRU), a mobile node, amobile, or something else.

Moreover, a base station used in the specification denotes a controlapparatus that controls one cell. However, a physical base station mayactually control a plurality of cells in a wireless communicationsystem, in which case the physical base station may be regarded asincluding one or more base stations used in the specification. Forexample, in the specification, different parameters being allocated to aplurality of cells should be understood as respective base stationsallocating different values to the cells. Also, the base station used inthe specification may be called by other names such as a base station, anode-B, an eNode-B, a base transceiver system (BTS), an access point, atransmission point, etc.

Hereinafter, example embodiments of the invention will be described indetail with reference to the accompanying drawings. In describing theinvention, to facilitate a comprehensive understanding of the invention,like numbers refer to like elements throughout the description of thefigures, and descriptions of elements are not repeated.

The 3GPP LTE system and the LTE-advanced system use a time domainstructure that is configured with a frame including ten subframes with alength of 1 ms.

When a data channel and a control channel are multiplexed in onesubframe, in order for a terminal to demodulate a received data channel,a base station needs to provide start position information of the datachannel to the terminal in a time domain.

The terminal may demodulate the data channel by using the start positioninformation received from the base station. Here, for example, the startposition information may be an index of a symbol configuring a subframe,and the symbol may be an OFDM symbol or an SC-FDMA symbol.

A method in which a base station transmits start position information toa terminal may be categorized into an implicit method and an explicitmethod.

The implicit method is a method in which a base station indirectlytransmits start position information through a control channel section,and requires that a data channel is transmitted from a symbol just nextto the control channel section. For example, in the 3GPP system, aterminal may receive the physical control format indicator channel(PCFICH), received from a base station, to determine a control channelsection of the base station.

When a plurality of base stations simultaneously transmit a data channelfor a specific terminal, a specific one of the base stations maytransmit information on the base stations that transmit the data channelto the terminal. Here, information on the base stations may include anidentifier (ID) of each of the base stations and reference signalinformation of each base stations. For example, in the 3GPP system, abase station ID may be a physical cell ID (PCI), and the referencesignal information may be the number of cell-specific reference signal(CRS) antennas or ports.

The terminal may determine a control channel section of each basestation that participates in transmission of the data channel, on thebasis of the information on the base stations that transmit the datachannel received from the specific base station. Also, the terminal maydetermine a control channel section of a base station that transmits acontrol channel. On the assumption that a data channel allocated to theterminal is transmitted from a symbol just next to a control channelsection that has the greatest value among the control channel section ofthe base station transmitting the control channel, the terminal maydemodulate the data channel. Here, the base station that transmits thecontrol channel to the terminal may or may not transmit the datachannel. In the 3GPP system, the terminal may receive the PCFICHtransmitted from the base station to determine the control channelsection of the base station.

Unlike an implicit method, in an explicit method, a base stationdirectly transmits start position information to a terminal. In awireless communication system, when the implicit method and the explicitmethod are simultaneously used, priority higher than that of theimplicit method may be given to the explicit method.

A base station transmits a data channel from the same start position asthat of start position information that is transmitted via the explicitmethod. A terminal demodulates the data channel on the basis of theexplicitly transmitted start position information.

The explicit method may be categorized into a semi-static signalingmethod and a dynamic signaling method.

The semi-static signaling method is a method in which a base stationtransmits start position information to a terminal through semi-staticsignaling, and particularly, when the start position information is notchanged for a certain time, the semi-static signaling method is useful.For example, in the 3GPP system, the semi-static signaling method mayallow a base station to transmit start position information to aterminal through high layer signaling or radio resource control (RRC)signaling.

The dynamic signaling method is a method in which a base stationtransmits start position information to a terminal through a controlchannel that is used to transmit allocation information of a datachannel, and when the start position information is changed for eachsubframe, the dynamic signaling method is useful. Hereinafter, thecontrol channel for transmitting the allocation information of the datachannel is referred to as an allocation information control channel. Forexample, in the 3GPP system, the allocation information control channelmay be the PDCCH.

A base station may allocate a control channel and a data channel to asubframe, and transmit start position information through the allocationinformation control channel. Hereinafter, a method of transmitting startposition information through the allocation information control channelin the method of transmitting and receiving a control channel accordingto an embodiment of the present invention will be described.

A first method includes defining a bit field representing start positioninformation in a payload of the allocation information control channel.Here, the payload of the allocation information control channel denotesa state before channel coding is applied. The bit size of the bit fieldmay vary according to a quantity of start position information.

A base station adds start position information into the bit field thatis defined in the payload of the allocation information control channel,and transmits the start position information with the bit field addedthereto to a terminal. Also, the base station may transmit semi-staticsignaling, which indicates whether the payload of the allocationinformation control channel includes the bit field representing thestart position information, to the terminal. The terminal varies thesize of the payload of the allocation information control channel todemodulate the allocation information control channel according to thesemi-static signaling received from the base station.

A second method involves using a bit field, which is defined for someother use in the payload of the allocation information control channel,as start position information. In a specific condition, at least one bitfield may not be used, and thus may be reused as start positioninformation.

A base station adds start position information into a bit field that isnot used in the payload of the allocation information control channel,and transmits the start position information with the bit field addedthereto to a terminal. Also, the base station may transmit semi-staticsignaling, which indicates whether the bit field (which is defined forsome other use in the payload of the allocation information controlchannel) is to be used as the start position information, to theterminal. The terminal demodulates the allocation information controlchannel on the basis of the semi-static signaling received from the basestation.

In a third method, a predefined mask is applied differently to cyclicredundancy check (CRC) of the payload of the allocation informationcontrol channel according to start position information. Here, thenumber of predefined masks may vary according to a quantity of startposition information. An embodiment of the third method may be expressedas Equation (1).

c _(k)=(p _(k) +x _(k) ^(RNTI) +x _(k) ^(SS))mod 2, k=0,1, . . . ,L−1

where p_(k) denotes CRC of the payload of the allocation informationcontrol channel, L denotes a CRC length, and x_(k) ^(RNTI) denotes atemporary ID (radio network temporary identifier (RNTI) of a terminal.As an example, in the 3GPP system, the temporary ID of the terminal maybe a cell RNTI (C-RNTI), a semi-persistent scheduling C-RNTI (SPSC-RNTI), or a temporary C-RNTI, and one terminal may have all of theC-RNTI, the SPS C-RNTI, and the temporary C-RNTI. x_(k) ^(SS) denotes aCRC mask based on start position information, and c_(k) denotes a CRCmask result value.

In Equation 1, x_(k) ^(RNTI) is included as one parameter for applyingthe CRC mask, in the CRC mask, but in another embodiment of the presentinvention, x_(k) ^(RNTI) may not be included in the CRC mask of thepayload of the allocation information control channel. Also, in anotherembodiment of the present invention, a mask that is not expressed inEquation (1) may be additionally added into the CRC mask of the payloadof the allocation information control channel.

As a detailed example in which Equation (1) is applied, when the CRClength is defined as 16 (i.e., L=16), the CRC mask based on the startposition information may be indicated as Table 1 or Table 2. In Table 1or Table 2, the start position information is expressed as 1, 2, and 3as an example, but the start position information and the CRC mask arenot limited to Table 1 or Table 2.

TABLE 1 CRC mask of start position information Start positioninformation <x₀ ^(SS), x₁ ^(SS), x₂ ^(SS), . . . , x₁₅ ^(SS)> 1 <0, 0,0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0> 2 <1, 1, 1, 1, 1, 1, 1, 1, 1,1, 1, 1, 1, 1, 1, 1> 3 <0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1>

TABLE 2 CRC mask of start position information Start positioninformation <x₀ ^(SS), x₁ ^(SS), x₂ ^(SS), . . . , x₁₅ ^(SS)> 1 <0, 0,0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0> 2 <0, 0, 0, 0, 0, 0, 0, 0, 0,0, 0, 0, 0, 0, 0, 1> 3 <0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0>

In Equation (1), a modulo operation is performed with the CRC mask(corresponding to the start position information) and the temporary IDof the terminal. When a modulo operation result of a CRC mask ofarbitrary start position information and a temporary ID of a specificterminal is equal to a modulo operation result of the CRC mask of thearbitrary start position information and a temporary ID of anotherterminal, a plurality of terminals can recognize an allocationinformation control channel for one specific terminal as theirallocation information control channels.

To prevent such a drawback, a base station needs to allocate a temporaryID to a terminal such that a modulo operation result of a temporary IDallocated to a specific terminal and a CRC mask of arbitrary startposition information differs from a modulo operation result of atemporary ID of another terminal and the CRC mask of the arbitrary startposition information.

That is, although a base station actually allocates only one temporaryID to a terminal, the base station does not allocate temporary ID(s)equal to “a quantity of start position information—1” to other terminalsbut rather reserves the temporary IDs. This denotes that a base stationvirtually allocates temporary ID(s) equal to a quantity of startposition information. For example, as shown in Table 1 and Table 2, whena quantity of start position information is three, a base stationactually allocates one temporary ID to a specific terminal, and reservestwo temporary IDs without allocating the two temporary IDs to otherterminals, thereby virtually allocating three temporary IDs to thespecific terminal.

A base station may or may not use the explicit method for transmittingstart position information to a terminal. The base station does not usea CRC mask of the start position information for a terminal that usesonly the implicit method without using the explicit method. Therefore,the base station needs to reserve temporary IDs that are not allocatedto another terminals. That is, it may be considered that the basestation actually and virtually allocates only one temporary ID to theterminal.

Moreover, the base station may divide a plurality of temporary IDs intotwo groups, for efficiently using the temporary IDs. One of the twogroups is a temporary ID group for terminals using the explicit methodand is a group (hereinafter referred to as a first group) that actuallyallocates only one temporary ID but virtually allocates temporary IDsequal to a quantity of start position information. The other of the twogroups is a temporary ID group for terminals using only the implicitmethod, and is a group (hereinafter referred to as a second group) thatactually or virtually allocates only one temporary ID.

When the base station intends to allocate a temporary ID to a terminalfor the first time, the base station cannot determine whether theterminal uses the explicit method or uses only the implicit method.Therefore, the base station allocates a temporary ID of the first orsecond group to the terminal. At this point, the temporary ID of thesecond group may be allocated to a terminal using the explicit method,and the temporary ID of the first group may be allocated to a terminalusing only the implicit method.

When the temporary ID of the second group is first allocated to theterminal using the explicit method, a plurality of terminals canrecognize an allocation information control channel for one specificterminal as their allocation information control channels.

To prevent such a drawback, the base station knows whether the terminaluses the explicit method or the implicit method, and when the temporaryID of the second group is first allocated to the terminal using theexplicit method, the base station may change the allocated temporary IDto the temporary ID of the first group.

Alternatively, when the number of temporary IDs of the first group isinsufficient, when the temporary ID of the first group is firstallocated to the terminal using only the implicit method, the basestation may change the temporary ID (which is first allocated to theterminal using only the implicit method) to the temporary ID of thefirst group.

In a fourth method, a base station additionally allocates differenttemporary IDs according to start position information, calculates a CRCvalue with the additionally allocated temporary IDs, and inserts the CRCvalue into the payload of the allocation information control channel.The number of temporary IDs which are additionally allocated by the basestation may vary based on a quantity of start position information.

The base station and a terminal may predefine start positioninformation. A temporary ID that the base station allocates to theterminal may be predefined as indicating specific start positioninformation. Subsequently, the base station may additionally allocate atemporary ID indicating other start position information to a terminalusing the explicit method. An embodiment of the fourth method may beexpressed as Equation (2).

c _(k)=(p _(k) +x _(k) ^(RNTI,n))mod 2, k=0,1, . . . ,L−1  (2)

where p_(k) denotes CRC of the payload of the allocation informationcontrol channel, L denotes a CRC length, c_(k) denotes a CRC mask resultvalue, and x_(k) ^(RNTI,n) denotes a temporary ID of a terminal based onstart position information. In an embodiment of the present invention,when it is assumed that start position information which a base stationand a terminal have predefined is 1, 2, and 3, the temporary ID of theterminal based on start position information may be expressed as inTable 3, for example. A temporary ID “x_(k) ^(RNTI,0)” that the basestation first allocates to the terminal may be predefined as being usedto indicate first start position information. Subsequently, the basestation may additionally allocate temporary IDs “x_(k) ^(RNTI,1)” and“x_(k) ^(RNTI,2)” indicating the other start position information “2”and “3” to terminals using the explicit method.

TABLE 3 Start position information Temporary ID 1 x_(k) ^(RNTI, 0) 2x_(k) ^(RNTI, 1) 3 x_(k) ^(RNTI, 2)

In Table 3, the start position information is expressed as 1, 2, and 3as an example, but the start position information and the temporary IDscorresponding thereto are not limited to Table 3.

In a fifth method, a base station applies different scrambling sequencesto the payload of the allocation information control channel accordingto start position information. The number of scrambling sequences mayvary according to a quantity of start position information. Here, eachof the scrambling sequences may be generated by changing a sequenceinitial value in the same sequence according to the start positioninformation. Also, the scrambling sequences may use different predefinedsequences according to the start position information. An embodiment ofthe fifth method may be expressed as Equation (3).

b _(k)=(a _(k) +s _(k))mod 2, k=0,1, . . . ,A−1  (3)

where a_(k) denotes the payload of the allocation information controlchannel, A denotes a payload length of the allocation informationcontrol channel, s_(k) denotes a scrambling sequence, and b_(k) denotesa result value that is obtained by scrambling the payload of theallocation information control channel. CRC of the payload of theallocation information control channel may be generated for thescrambled result value.

When one base station transmits a data channel and a control channel toa terminal, start position information may be transmitted in only theimplicit method. However, when a base station that transmits the datachannel to the terminal differs from a base station that transmits thecontrol channel to the terminal, the start position informationtransmitted via the implicit method can be inaccurate.

FIG. 1 is a conceptual diagram illustrating an example of a wirelesscommunication environment in which it is necessary to explicitlytransmit start position information. FIG. 1, for example, illustrates acase in which a base station transmitting the data channel differs froma base station transmitting the control channel.

In FIG. 1, a first base station 110 transmits a control channel to aterminal 150, and a second base station 130 transmits a data channel tothe terminal 150.

The control channel of the first base station 110 transmitting thecontrol channel consists of two symbols, but the control channel of thesecond base station 130 transmitting the data channel consists of threesymbols.

In an environment that is as illustrated in FIG. 1, when a base stationtransmits start position information via the implicit method, theterminal 150 performs demodulation, on the assumption that a datachannel starts from the third symbol of a subframe on the basis of thecontrol channel of the first base station 110.

However, an actual data channel starts from the fourth symbol of thesubframe, and thus, it is quite possible that the terminal 150 fails todemodulate the data channel.

Accordingly, in the environment of FIG. 1, a base station may transmitstart position information via the explicit method, for transmittingaccurate start position information to the terminal 150.

FIG. 2 is a conceptual diagram illustrating another example of awireless communication environment in which it is necessary toexplicitly transmit start position information, and as an example,illustrates a case in which a plurality of base stations 110 and 130transmit a data channel to a terminal 150, and one base station 110transmits a control channel to the terminal 150.

When a plurality of base stations transmit a data channel to theterminal 150 and one base station transmits a control channel to theterminal 150, the transmission of start position information via theimplicit method may be inaccurate.

In FIG. 2, the first base station 110 transmits a control channel and adata channel to the terminal 150, and the second base station 130transmits a data channel to the terminal 150. The first and second basestations 110 and 120 need to transmit the data channel to the terminal150 by using the same resource, and thus transmit the data channel fromthe fourth symbol of a subframe with respect to the control channelsection of the second base station 130 having the longer control channelsection of the control channel sections of the first and second basestations 110 and 130.

However, the control channel of the first base station 110 transmittingthe control channel consists of two symbols, and thus, when the firstbase station 110 transmits start position information via the implicitmethod, the terminal performs demodulation on the assumption that thedata channel starts from the third symbol. On the other hand, an actualdata channel starts from the fourth symbol, and thus, the terminal 150mostly fails to demodulate the data channel.

Accordingly, in the environment of FIG. 2, a base station may transmitstart position information via the explicit method, for transmittingaccurate start position information to the terminal 150.

An environment that requires the implicit method or the explicit methodfor transmitting start position information is a wireless communicationenvironment in the above-described embodiments of the present invention.However, according to the present invention, the implicit method or theexplicit method may be applied to environments other than theabove-described wireless communication environment.

When a base station transmitting a data channel differs from a basestation transmitting a control channel as illustrated in FIG. 1, or whena plurality of base stations transmit a data channel as illustrated inFIG. 2, the reference signal arrangement of a base station transmittingthe control channel may differ from the reference signal arrangement ofa base station transmitting the data channel.

The reference signal arrangement may change according to the frequencyshift of a reference signal, the number of reference signal antennas orports, or whether a subframe in which a data channel is transmitted is amulticast-broadcast single frequency network (MBSFN) subframe or not.

A base station which transmits a control channel to a terminal maytransmit MBSFN subframe information, as information on base stationstransmitting a data channel, to a terminal. Here, the base station maytransmit the MBSFN subframe information in the semi-static signalingmethod or the dynamic signaling method.

First, a method of transmitting the MBSFN subframe information throughsemi-static signaling is one in which a base station transmits the MBSFNsubframe information to a terminal through semi-static signaling. Forexample, in the 3GPP system, semi-static signaling may be higher layersignaling or RRC signaling.

The MBSFN subframe information transmitted through the semi-staticsignaling method may become an MBSFN subframe pattern for a certaintime. Here, it is assumed that a previous MBSFN subframe pattern isrepeated until new MBSFN subframe information is transmitted to aterminal.

Base stations transmitting MBSFN subframe information are base stationsrelevant to the transmission of a data channel, and some of the basestations may not actually transmit the data channel to a terminal. Forexample, in the 3GPP system, the base stations may be a CoMP cooperatingset.

A method of transmitting MBSFN subframe information through the dynamicsignaling method includes defining a bit field representing the MBSFNsubframe information in the payload of the allocation informationcontrol channel, and using the defined bit field.

In the dynamic signaling method, the MBSFN subframe information mayconsist of bitmap information indicating whether the subframe of eachbase station transmitting a data channel is an MBSFN subframe or not.Here, base stations transmitting the MBSFN subframe information are basestations that transmit a data channel to a terminal. For example, in the3GPP system, the base stations may be the CoMP transmission set.

A downlink subframe may be configured by time-division-multiplexing adownlink physical control channel and a downlink physical data channel.

FIG. 3 is a conceptual diagram illustrating a configuration of adownlink subframe that is used in a method of transmitting and receivinga control channel according to an embodiment of the present invention.

As illustrated in FIG. 3, the downlink subframe may be configured bytime-division-multiplexing the downlink physical control channel and thedownlink physical data channel, and an enhanced downlink physicalcontrol channel may be added into a downlink physical data channelsection and transmitted. Hereinafter, the enhanced downlink physicalcontrol channel is referred to as an ePDCCH. In the 3GPP system, thedownlink physical control channel may be a PDCCH.

One ePDCCH may consist of one enhanced control channel element or aplurality of enhanced control channel elements. Hereinafter, an enhancedcontrol channel element is referred to as an eCCE. One eCCE may beconfigured with a plurality of resource elements. Here, a resourceelement is the same as the resource element, or RE, of the 3GPP system.

One virtual resource block pair may include a plurality of eCCEs. Also,one eCCE may be included in one virtual resource block. Here, thevirtual resource block and the virtual resource block pair are the sameas a virtual resource block (VRB) and a VRB pair in the 3GPP system,respectively.

FIGS. 4 to 10 are conceptual diagrams illustrating a configuration of aneCCE and a downlink demodulation reference signal when a plurality ofeCCEs exist in one virtual resource block pair.

In FIGS. 4 to 10, it is assumed that the number of OFDM symbols of thedownlink physical control channel is two, and the number of transmissionantenna ports for a downlink cell-specific reference signal is four. AneCCE is transmitted from a position from which the downlinkcell-specific reference signal is not transmitted in the eCCE of asubframe according to the number of transmission antenna ports for thedownlink cell-specific reference signal.

FIG. 4 illustrates a configuration of an eCCE and a downlinkdemodulation reference signal when one downlink subframe consists offourteen OFDM symbols and is a normal subframe, in a method oftransmitting and receiving a control channel according to an embodimentof the present invention.

Moreover, FIG. 4 illustrates a configuration of an eCCE and a downlinkdemodulation reference signal when three eCCEs exist in one virtualresource block pair.

FIG. 5 illustrates a configuration of an eCCE and a downlinkdemodulation reference signal when one downlink subframe consists offourteen OFDM symbols and is a normal subframe, in a method oftransmitting and receiving a control channel according to anotherembodiment of the present invention, and illustrates a configuration ofan eCCE and a downlink demodulation reference signal when three eCCEsexist in one virtual resource block pair.

FIGS. 4 and 5 differ in position of the downlink demodulation referencesignal on the frequency axis.

FIG. 6 illustrates a configuration of an eCCE and a downlinkdemodulation reference signal when one downlink subframe consists offourteen OFDM symbols and is a normal subframe, in a method oftransmitting and receiving a control channel according to anotherembodiment of the present invention, and illustrates a configuration ofan eCCE and a downlink demodulation reference signal when four eCCEsexist in one virtual resource block pair.

When the subframe of each of FIGS. 4 to 6 is an MBSFN subframe, adownlink cell-specific reference signal is not transmitted in each eCCEof FIGS. 4 to 6, and an eCCE is transmitted to the position of adownlink cell-specific reference signal.

FIG. 7 illustrates a configuration of an eCCE and a downlinkdemodulation reference signal when one downlink subframe consists offourteen OFDM symbols and is a special subframe, in a method oftransmitting and receiving a control channel according to anotherembodiment of the present invention.

As an example, FIG. 7 illustrates a configuration of an eCCE and adownlink demodulation reference signal when a downlink part (downlinkpilot time slot (DwPTS)) is configured with eleven symbols among thefourteen OFDM symbols and includes four eCCEs.

FIG. 8 illustrates a configuration of an eCCE and a downlinkdemodulation reference signal when one downlink subframe consists offourteen OFDM symbols and is a special subframe, in a method oftransmitting and receiving a control channel according to anotherembodiment of the present invention.

As an example, FIG. 8 illustrates a configuration of an eCCE and adownlink demodulation reference signal when a downlink part (DwPTS) isconfigured with nine symbols among the fourteen OFDM symbols andincludes four eCCEs.

FIG. 9 illustrates a configuration of an eCCE and a downlinkdemodulation reference signal when one downlink subframe consists oftwelve OFDM symbols and is a normal subframe, in a method oftransmitting and receiving a control channel according to anotherembodiment of the present invention,

As an example, FIG. 9 illustrates a configuration of an eCCE and adownlink demodulation reference signal when four eCCEs exist in onevirtual resource block pair. For example, when a subframe is an MBSFNsubframe, the downlink cell-specific reference signal of FIG. 9 is nottransmitted, and an eCCE is transmitted to the position of the downlinkcell-specific reference signal.

FIG. 10 illustrates a configuration of an eCCE and a downlinkdemodulation reference signal when one downlink subframe consists oftwelve OFDM symbols and is a special subframe, in a method oftransmitting and receiving a control channel according to anotherembodiment of the present invention.

As an example, FIG. 10 illustrates a configuration of an eCCE and adownlink demodulation reference signal when a downlink part (DwPTS) ofthe special subframe is configured with eight symbols among the fourteenOFDM symbols, and the configuration of the eCCE and downlinkdemodulation reference signal may change according to the number of OFDMsymbols configuring the downlink part.

In the above-described configuration of the subframe, when a subframe isa normal subframe or when a subframe is an MBSFN subframe, a zeropowerchannel state information reference signal (CSI-RS) and/or anon-zeropower channel state information reference signal (CSI-RS) may bedisposed in an eCCE, in which case an eCCE is not transmitted from theposition of the zeropower CSI-RS and/or the position of non-zeropowerCSI-RS.

An ePDCCH may consist of one eCCE or a plurality of eCCEs. Hereinafter,the number of eCCEs configuring one ePDCCH is referred to as anaggregation level. For example, the aggregation level may consist of aset such as 1, 2, 4, 8 or the like. Hereinafter, a set of eCCEs that aterminal needs to search and that is a region in which ePDCCH candidatesare transmittable is referred to as a search space.

The search space may change according to terminals or the aggregationlevel of an ePDCCH. Also, since the format of an ePDCCH is not known toa terminal in advance, the terminal may change the aggregation level tofind an ePDCCH (which is transmitted from a base station) through blinddecoding, and the number of blind decodings may vary according to theaggregation level.

The search space may be a localized type search space or a distributedtype search space according to terminals. A base station may inform aterminal of whether the search space is the localized type search spaceor the distributed type search space through higher layer signaling foreach terminal. In the 3GPP system, higher layer signaling for eachterminal may be RRC signaling.

The localized type search space may be configured as follows, forobtaining a frequency selective scheduling gain.

First, in all aggregation levels (for example, 1, 2, 4, 8), each ePDCCHmay consist of adjacent eCCEs. Such an operation may be performed by abase station. It is assumed by a terminal that the same precoding isapplied to a plurality of eCCEs in each ePDCCH candidate. Also, the basestation may set an eCCE-unit offset between ePDCCH candidates, and theoffset may change according to aggregation level. Here, the offset maybe a positive integer including zero.

Moreover, a base station may set an eCCE-unit offset for each terminal,for efficiently using the resource of the localized type search space.Here, the offset for each terminal may be a positive integer includingzero.

When an aggregation level is L, i_(offset,L) indicating the offset foreach terminal may be expressed as Equation (4).

i _(offset,L)=(ID)mod K _(offset,L)  (4)

where ID denotes an identifier that a base station gives to a terminal.In the 3GPP system, the identifier (ID) is an RNTI, and may be a C-RNTIor an SPS C-RNTI. K_(offset,L) denotes the number of offsets betweenePDCCH candidates when an aggregation level is L, and may have differentvalues according to the aggregation level “L”.

A base station may inform each terminal of an offset for each terminalthrough higher layer signaling for each terminal. In the 3GPP system,higher layer signaling for each terminal may be RRC signaling. Also, thebase station may set the same offset for each terminal or set differentoffsets according to aggregation level.

Higher layer signaling for each terminal may include an offset for eachterminal by aggregation level, and the same offset for each terminal maybe included in all aggregation levels. Here, an offset for each terminalmay be zero according to aggregation level, and the offset for eachterminal of an aggregation level whose offset for each terminal is zeromay not be included in higher layer signaling for each terminal.

A base station may inform a terminal of one virtual resource block pairor virtual resource block through higher layer signaling for eachterminal, in order for the terminal to determine a search space. Also,the base station may inform the terminal of one virtual resource blockset consisting of a plurality of virtual resource blocks or a pluralityof virtual resource block pairs through higher layer signaling for eachterminal, in order for the terminal to determine the search space.

The mapping of the physical resource block of a virtual resource blockmay be based on a resource allocation type “0”, a resource allocationtype “1”, and a resource allocation type “2” that are defined in thestandard of the 3GPP system. In the 3GPP system, higher layer signalingfor each terminal may be RRC signaling. When a base station may inform aterminal of one virtual resource block set consisting of a plurality ofvirtual resource blocks or a plurality of virtual resource block pairsthrough higher layer signaling for each terminal in order for theterminal to determine a search space, the localized type search spacemay be set as expressed in Equation (5).

n _(eCC) ^(ePDCCH)=(L·(m·K _(offset,L) +i _(offset,L))+i)mod N wherei=0,1, . . . ,L−1 and m=0,1, . . . ,M _(L)−1  (5)

where n_(eCCE) ^(ePDCCH) denotes the index of an eCCE in which an ePDCCHcandidate “m” having an aggregation level “L” is disposed. N denotes thenumber of eCCEs configuring one virtual resource block set that a basestation transmits to a terminal, and an eCCE index in a virtual resourceblock set is 0, 1, . . . , N−1. L denotes the aggregation level of aneCCE, m denotes the index of an ePDCCH candidate, and i_(offset,L)denotes an offset for each terminal when an aggregation level is L.K_(offset,L) denotes an offset between ePDCCH candidates when theaggregation level is L, and i denotes an eCCE index configuring anePDCCH candidate having an aggregation level “L”. Also, M_(L) denotesthe number of ePDCCH candidates having an aggregation level “L”. Asexpressed in Equation (5), respective ePDCCH candidates may betransmitted to L number of successive eCCEs.

Alternatively, when a base station may inform a terminal of one virtualresource block pair or virtual resource block in order for the terminalto determine a search space, the localized type search space may be setas expressed in Equation (6).

n _(eCCE) ^(ePDCCH)=(L·(m·K _(offset,L) +i _(offset,L))+i) where i=0,1,. . . ,L−1 and m=0,1, . . . ,M _(L)−1  (6)

where n_(eCCE) ^(ePDCCH) denotes the index of an eCCE in which an ePDCCHcandidate “m” having an aggregation level “L” is disposed. One virtualresource block pair or virtual resource block of which a base stationhas informed a terminal corresponds to a position in which an eCCE “0”that is the lowest index in a search space is mapped, and a plurality ofvirtual resource blocks or virtual resource block pairs having thesecond greatest value after the index of the virtual resource block pairor virtual resource block of which the base station has informed theterminal configure a search space successively. An ePDCCH in whichi_(offset,L)=0 and m=0 is transmitted to the virtual resource block pairor virtual resource block of which the base station has informed theterminal. L denotes the aggregation level of an eCCE, m denotes theindex of an ePDCCH candidate, and i_(offset,L) denotes an offset foreach terminal when an aggregation level is L. K_(offset,L) denotes anoffset between ePDCCH candidates when the aggregation level is L, and idenotes an eCCE index configuring an ePDCCH candidate having anaggregation level “L”. As expressed in Equation (6), respective ePDCCHcandidates may be transmitted to L number of successive eCCEs.

FIGS. 11 to 14 are conceptual diagrams illustrating a configurationexample of a localized type search space in a method of transmitting andreceiving a control channel according to an embodiment of the presentinvention.

FIG. 11 is a diagram illustrating a configuration example of a localizedtype search space in a method of transmitting and receiving a controlchannel according to an embodiment of the present invention.

In FIG. 11, the aggregation level of an eCCE is assumed to be L=1, 2, 4,and 8. In the drawing, a number illustrated in each ePDCCH candidatedenotes the index “m” of each ePDCCH candidate. Also, the number ofePDCCH candidates is assumed to be M₁=M₂=6 and M₄=M₈=2. Offsets betweenePDCCH candidates are assumed to be K_(offset,1)=4,K_(offset,2)=K_(offset,4)=2, and K_(offset,8)=1. An offset for eachterminal is assumed to bei_(offset,1)=i_(offset,2)=i_(offset,4)=i_(offset,8)=0.

FIG. 12 is a diagram illustrating a configuration example of a localizedtype search space in a method of transmitting and receiving a controlchannel according to another embodiment of the present invention.

In FIG. 12, the aggregation level of an eCCE is assumed to be L=1, 2, 4,and 8. In the drawing, a number illustrated in each ePDCCH candidatedenotes the index “m” of each ePDCCH candidate. Also, the number ofePDCCH candidates is assumed to be M₁=M₂=6 and M₄=M₈=2. Offsets betweenePDCCH candidates are assumed to be K_(offset,1)=4,K_(offset,2)=K_(offset,4)=2, and K_(offset,8)=1. An offset for eachterminal is assumed to be i_(offset,1)=2, i_(offset,2)=i_(offset,4)=1,and i_(offset,8)=0.

FIG. 13 is a diagram illustrating a configuration example of a localizedtype search space in a method of transmitting and receiving a controlchannel according to another embodiment of the present invention.

In FIG. 13, the aggregation level of an eCCE is assumed to be L=1, 2, 4,and 8. In the drawing, a number illustrated in each ePDCCH candidatedenotes the index “m” of each ePDCCH candidate. Also, the number ofePDCCH candidates is assumed to be M₁=8, M₂=4, and M₄=M₈=2. Offsetsbetween ePDCCH candidates are assumed to beK_(offset,1)=K_(offset,2)=K_(offset,4)=2, and K_(offset,8)=1. An offsetfor each terminal is assumed to bei_(offset,1)=i_(offset,2)=i_(offset,4)=i_(offset,8)=0.

FIG. 14 is a diagram illustrating a configuration example of a localizedtype search space in a method of transmitting and receiving a controlchannel according to another embodiment of the present invention.

In FIG. 14, the aggregation level of an eCCE is assumed to be L=1, 2, 4,and 8. In the drawing, a number illustrated in each ePDCCH candidatedenotes the index “m” of each ePDCCH candidate. Also, the number ofePDCCH candidates is assumed to be M₁=8, M₂=4, and M₄=M₈=2. Offsetsbetween ePDCCH candidates are assumed to beK_(offset,1)=K_(offset,2)=K_(offset,4)=2, and K_(offset,8)=1. An offsetfor each terminal is assumed to bei_(offset,1)=i_(offset,2)=i_(offset,4)=1, and i_(offset,8)=0.

The distributed type search space may be configured as follows, forobtaining a frequency diversity gain.

First, in all aggregation levels (for example, 1, 2, 4, 8), each ePDCCHmay consist of distributed eCCEs that are not adjacent to one another.An eCCE-unit offset between a plurality of eCCEs configuring each ePDCCHcandidate is necessary for configuring each ePDCCH candidate withdistributed eCCEs, and the offset may change according to aggregationlevel. Here, the offset may be a positive integer including zero.

It is assumed by a terminal that different precodings are applied to aplurality of eCCEs included in each ePDCCH candidate.

Moreover, there may be an eCCE-unit offset between ePDCCH candidates,and the offset may change according to aggregation level. Here, theoffset may be a positive integer including zero.

Moreover, there may be an eCCE-unit offset for each terminal, forefficiently using the distributed type search space. Here, the offsetfor each terminal may be a positive integer including zero. The offsetfor each terminal in the distributed type search space may be configuredas expressed in Equation (4), as in the above-described offset for eachterminal.

A base station may inform a terminal of an offset for each terminalthrough higher layer signaling for each terminal. In the 3GPP system,higher layer signaling for each terminal may be RRC signaling. Offsetsfor respective terminals may be the same or may differ. Higher layersignaling for each terminal may include an offset for each terminal byaggregation level, and the same one offset for each terminal may beincluded in all aggregation levels. An offset for each terminal may bezero according to aggregation level, and the offset for each terminal ofan aggregation level whose offset for each terminal is zero may not beincluded in higher layer signaling for each terminal.

A base station may inform a terminal of one virtual resource block pairor virtual resource block through higher layer signaling for eachterminal, in order for the terminal to determine a search space. Also,the base station may inform the terminal of one virtual resource blockset consisting of a plurality of virtual resource blocks or a pluralityof virtual resource block pairs through higher layer signaling for eachterminal, in order for the terminal to determine the search space.

The mapping of the physical resource block of a virtual resource blockmay be based on a resource allocation type “0”, a resource allocationtype “1”, and a resource allocation type “2” that are defined in thestandard of the 3GPP system. In the 3GPP system, higher layer signalingfor each terminal may be RRC signaling.

When a base station may inform a terminal of one virtual resource blockset consisting of a plurality of virtual resource blocks or a pluralityof virtual resource block pairs through higher layer signaling for eachterminal in order for the terminal to determine a search space, thedistributed type search space may be set as expressed in Equation (7).

n _(eCCE) ^(ePDCCH)=(m·K _(offset,L) +i _(offset,L) +i·D _(offset,L))modN where i=0,1, . . . ,L−1 and m=0,1, . . . ,M _(L)−1  (7)

where n_(eCCE) ^(ePDCCH) denotes the index of an eCCE in which an ePDCCHcandidate “m” having an aggregation level “L” is disposed. N denotes thenumber of eCCEs configuring one virtual resource block set that a basestation transmits to a terminal, and an eCCE index in a virtual resourceblock set is 0, 1, . . . , N−1. L denotes the aggregation level of aneCCE, and m denotes the index of an ePDCCH candidate. Also, i_(offset,L)denotes an offset for each terminal when an aggregation level is L.K_(offset,L) denotes an offset between ePDCCH candidates when theaggregation level is L.

D_(offset,L) denotes an offset between a plurality of eCCEs in eachePDCCH candidate when an aggregation level is L. i denotes an eCCE indexconfiguring an ePDCCH candidate having an aggregation level “L”.Respective ePDCCH candidates may be transmitted to L number ofdistributed eCCEs.

Moreover, when a base station may inform a terminal of one virtualresource block pair or virtual resource block in order for the terminalto determine a search space, the distributed type search space may beset as expressed in Equation (8).

n _(eCCE) ^(ePDCCH) =m·K _(offset,L) +i _(offset,L) +i·D _(offset,L)where i=0,1, . . . ,L−1 and m=0,1, . . . ,M _(L)−1  (8)

where n_(eCCE) ^(ePDCCH) denotes the index of an eCCE in which an ePDCCHcandidate “m” having an aggregation level “L” is disposed. One virtualresource block pair or virtual resource block of which a base stationhas informed a terminal corresponds to a position in which an eCCE “0”that is the lowest index in a search space is mapped, and a plurality ofvirtual resource blocks or virtual resource block pairs having thesecond greatest value after the index of the virtual resource block pairor virtual resource block of which the base station has informed theterminal configure a search space successively.

An ePDCCH in which i_(offset,L)=0 and m=0 is transmitted to the virtualresource block pair or virtual resource block of which the base stationhas informed the terminal. L denotes the aggregation level of an eCCE, mdenotes the index of an ePDCCH candidate, and i_(offset,L) denotes anoffset for each terminal when an aggregation level is L. K_(offset,L)denotes an offset between ePDCCH candidates when the aggregation levelis L. Also, D_(offset,L) denotes an offset between a plurality of eCCEsin each ePDCCH candidate when an aggregation level is L. i denotes aneCCE index configuring an ePDCCH candidate having an aggregation level“L”. As expressed in Equation (8), respective ePDCCH candidates may betransmitted to L number of distributed eCCEs.

FIGS. 15 to 18 are conceptual diagrams illustrating a configurationexample of a distributed type search space in a method of transmittingand receiving a control channel according to an embodiment of thepresent invention.

FIG. 15 is a diagram illustrating a configuration example of adistributed type search space in a method of transmitting and receivinga control channel according to an embodiment of the present invention.

In FIG. 15, the aggregation level of an eCCE is assumed to be L=1, 2, 4,and 8. In the drawing, a number illustrated in each ePDCCH candidatedenotes the index “m” of each ePDCCH candidate. Also, the number ofePDCCH candidates is assumed to be M₁=M₂=6 and M₄=M₈=2. Offsets betweenePDCCH candidates are assumed to be K_(offset,1)=4,K_(offset,2)=K_(offset,4)=2, and K_(offset,8)=1. Also, offsets between aplurality of eCCEs in an ePDCCH candidate are assumed to beD_(offset,1)=1, D_(offset,2)=12, D_(offset,4)=4, and D_(offset,8)=2, andan offset for each terminal is assumed to beD_(offset,1)=i_(offset,2)=i_(offset,4)=i_(offset,8)=0.

FIG. 16 is a diagram illustrating a configuration example of adistributed type search space in a method of transmitting and receivinga control channel according to another embodiment of the presentinvention.

In FIG. 16, the aggregation level of an eCCE is assumed to be L=1, 2, 4,and 8. In the drawing, a number illustrated in each ePDCCH candidatedenotes the index “m” of each ePDCCH candidate. Also, the number ofePDCCH candidates is assumed to be M₁=M₂=6 and M₄=M₈=2. Offsets betweenePDCCH candidates are assumed to be K_(offset,1)=4,K_(offset,2)=K_(offset,4)=2, and K_(offset,8)=1. Also, offsets between aplurality of eCCEs in an ePDCCH candidate are assumed to be D_(offset,1)⁼¹, D_(offset,2)=12, D_(offset,4)=4, and D_(offset,8)=2, and an offsetfor each terminal is assumed to be i_(offset,1)=2, i_(offset,2) =i_(offset,4)=1, and i_(offset,8)=0.

FIG. 17 is a diagram illustrating a configuration example of adistributed type search space in a method of transmitting and receivinga control channel according to another embodiment of the presentinvention.

In FIG. 17, the aggregation level of an eCCE is assumed to be L=1, 2, 4,and 8. In the drawing, a number illustrated in each ePDCCH candidatedenotes the index “m” of each ePDCCH candidate. Also, the number ofePDCCH candidates is assumed to be M₁=8, M₂=4, and M₄=M₈=2. Offsetsbetween ePDCCH candidates are assumed to beK_(offset,1)=K_(offset,2)=K_(offset,4)=2, and K_(offset,8)=1. Also,offsets between a plurality of eCCEs in an ePDCCH candidate are assumedto be D_(offset,1)=1, D_(offset,2)=8, D_(offset,4)=4, andD_(offset,8)=2, and an offset for each terminal is assumed to bei_(offset,1)=i_(offset,2)=i_(offset,4)=i_(offset,8)=0.

FIG. 18 is a diagram illustrating a configuration example of adistributed type search space in a method of transmitting and receivinga control channel according to another embodiment of the presentinvention.

In FIG. 18, the aggregation level of an eCCE is assumed to be L=1, 2, 4,and 8. In the drawing, a number illustrated in each ePDCCH candidatedenotes the index “m” of each ePDCCH candidate. Also, the number ofePDCCH candidates is assumed to be M₁=8, M₂=4, and M₄=M₈=2. Offsetsbetween ePDCCH candidates are assumed to beK_(offset,1)=K_(offset,2)=K_(offset,4)=2, and K_(offset,8)=1. Also,offsets between a plurality of eCCEs in an ePDCCH candidate are assumedto be D_(offset,1)=1, D_(offset,2)=8, D_(offset,4)=4, andD_(offset,8)=2, and an offset for each terminal is assumed to bei_(offset,1)=i_(offset,2)=i_(offset,4)=1, and i_(offset,8)=0.

As described above, the ePDCCH supports localized transmission anddistributed transmission, but the downlink physical control channelsupports only the distributed type. Also, the search space of a terminalmay be divided into a terminal-common (UE-common) search space and aterminal-specific (UE-specific) search space. In the terminal-commonsearch space a terminal may receive control information for a pluralityof terminals, but in the terminal-specific search space a terminal mayreceive control information for one specific terminal.

In a legacy system capable of transmitting and receiving only thedownlink physical control channel, a base station transmits the controlinformation of the terminal-common search space and the controlinformation of the terminal-specific search space through only thedownlink physical control channel. On the other hand, in an enhancedsystem capable of transmitting and receiving the ePDCCH, a base stationmay transmit the control information of the terminal-common search spaceand the control information of the terminal-specific search spacethrough the downlink physical control channel or the ePDCCH.Hereinafter, a terminal incapable of transmitting and receiving theePDCCH is referred to as a legacy terminal, and a terminal capable oftransmitting and receiving the ePDCCH is referred to as an enhancedterminal.

The enhanced system supports the legacy terminal as well as the enhancedterminal, and thus, in the enhanced system, a base station and aterminal may transmit and receive the downlink physical control channel.

A transmission type and a channel for transmitting the controlinformation of a search space in the enhanced system in which thedownlink physical control channel and the ePDCCH have been defined willbe described in detail below. Also, an operation in which the enhancedterminal receives the control information of the search space will bedescribed in detail. In the terminal-common search space a terminal mayreceive common control information for both the enhanced terminal andthe legacy terminal. Accordingly, a base station may transmit the commoncontrol information through the downlink physical control channel, forsupporting the legacy terminal. Depending on system configuration andenvironment, the base station may not transmit the downlink physicalcontrol channel in a specific component carrier. Also, the base stationmay transmit the downlink physical control channel, but the enhancedterminal may not receive the downlink physical control channel. In thiscase, the base station may transmit the common control informationthrough the ePDCCH, for the enhanced terminal. As described above, theenhanced terminal may or may not receive the downlink physical controlchannel depending on system configuration and environment.

A method in which the enhanced terminal receives a channel fortransmitting the common control information may be largely categorizedinto three methods.

A first method is a method in which the enhanced terminal receivescommon control information through only the downlink physical controlchannel. A second method is a method in which the enhanced terminalreceives common control information through only the ePDCCH. To thisend, a base station may transmit the same common control informationthrough the downlink physical control channel or the ePDCCH. A thirdmethod is a method in which a base station establishes a channel(downlink physical control channel or ePDCCH) through which commoncontrol information is received, to a terminal.

In the terminal-common search space a terminal may receive commoncontrol information for a plurality of terminals, and thus, distributedtransmission is more effective than localized transmission. Accordingly,when a base station transmits the common control information through theePDCCH, the ePDCCH may have a distributed type.

In the terminal-specific search space a terminal may receive two kindsof control information. One of the two kinds of control information iscontrol information based on the transmission mode of a physical datachannel, and the other is fallback control information irrelevant to thetransmission mode of the physical data channel. For example, in the 3GPPsystem, the physical data channel may be a PDSCH or a PUSCH, and thefallback control information may be a downlink control information (DCI)format lA or a DCI format 0.

A base station may transmit control information that is transmitted inthe terminal-specific search space, through the downlink physicalcontrol channel or the ePDCCH. The downlink physical control channelenables distributed transmission, but the ePDCCH enables localizedtransmission or distributed transmission.

A transmission type effective for control information based on thetransmission mode of the physical data channel may be the localized typeor the distributed type according to the transmission mode of thephysical data channel. A transmission type effective for the fallbackcontrol information is the distributed type in general, but may be thelocalized type depending on conditions.

A transmission scheme may be classified as shown in Table 4, accordingto the kinds of control information, the channels for transmitting thecontrol information, and the transmission types of the channels throughwhich the control information is transmitted.

TABLE 4 Control information based on physical data Fallback controltransmission mode information First trans- Downlink physical controlDownlink physical control mission scheme channel-distributed typechannel-distributed type Second trans- ePDCCH-distributed typeePDCCH-distributed type mission scheme Third trans- ePDCCH-localizedtype Downlink physical control mission scheme channel-distributed typeFourth trans- ePDCCH-localized type ePDCCH-distributed type missionscheme Fifth trans- ePDCCH-localized type ePDCCH-localized type missionscheme

All or some of the five transmission schemes classified in Table 4 maybe defined in the enhanced system.

Hereinafter, a plurality of transmission schemes capable of beingdefined in the enhanced system will be described in detail.

The first transmission scheme is necessary when the enhanced terminalcommunicates with a base station for the legacy system, and thus may beincluded in the enhanced system.

The second transmission scheme uniquely has the distributed type usingthe ePDCCH, and thus may be included in the enhanced system.

The following three methods may be used for adding the third to fifthtransmission schemes into the enhanced system.

In a first method, only the third and fourth transmission schemes areadded into the enhanced system.

In a second method, only the fourth transmission scheme is added intothe enhanced system.

In a third method, only the fifth transmission scheme is added into theenhanced system. Here, in the first and second methods, the transmissiontypes of channels for transmitting control information differ accordingto the kind of the control information (fallback control information orcontrol information based on the physical data transmission mode).Accordingly, the terminal-specific search space may be divided into asearch space for control information based on the physical datatransmission mode, and a search space for the fallback controlinformation. A base station may transmit resource block information,which configures each terminal-specific search space based on controlinformation, to a terminal through higher layer signaling. In each ofthe search spaces, the number of blind decodings performed by theenhanced terminal may differ. For the ePDCCH, the number of blinddecodings may be implicitly determined according to the size of aresource block configuring a search space.

Moreover, in the first method, the fallback control information may betransmitted through the downlink physical control channel or the ePDCCH,and thus, a base station may transmit establishment information on achannel, through which the fallback control information is transmitted,to a terminal through higher layer signaling.

The third method has only the ePDCCH-localized type as the transmissiontype of a channel through which control information is transmitted,irrespective of the kind of the control information. Accordingly, onlyone terminal-specific search space is required to be defined. A basestation may transmit resource block information that configures theterminal-specific search space to a terminal through higher layersignaling.

While example embodiments of the present invention and their advantageshave been described in detail, it should be understood that variouschanges, substitutions and alterations may be made herein withoutdeparting from the scope of the invention.

What is claimed is:
 1. A method of transmitting and receiving a controlchannel, which is performed in a data transmission apparatus, the methodcomprising: allocating a data channel to a radio resource; adding startposition information of the data channel into a payload of a controlchannel; and signaling indication information on the start positioninformation added into the payload of the control channel.